The present invention relates to a gas turbine plant, and in particular, to a gas turbine plant which previously heats a fuel supplied to a gas turbine combustor of the gas turbine plant and enhances a quantity of heat so as to improve a plant heat (thermal) efficiency.
In a gas turbine plant, it has been known that the plant heat efficiency is improves if an inlet combustion temperature of a gas turbine is made high. The plant heat efficiency is calculated from a ratio of a gas turbine power to a fuel supplied to a gas turbine combustor.
Therefore, how to reduce a fuel to be supplied to the gas turbine combustor, or how to enhance an output of the gas turbine is an important matter in order to improve the plant heat efficiency.
In view of the gas turbine output power in the light of the improvement of the plant heat efficiency, there is a problem of an increase in a power per unit combustion gas flow (specific power). However, an improvement of flow characteristic of a gas turbine blade and a reduction in other mechanical loss have already reached the limit, and it is difficult to greatly improve the flow characteristic and reduce the mechanical loss.
On the other hand, in order to reduce fuel consumption so as to improve the plant heat efficiency, it is important to improve a quantity of heat of fuel itself.
Recently, there has been disclosed Japanese Patent No. 2540646 as means for improving the quantity of heat of fuel itself. As shown in FIG. 29, the Japanese Patent No. 2540646 relates to a so-called multi-shaft type combined cycle power generation plant which is constructed in such a manner that a shaft of a gas turbine plant 2 connected to an exhaust heat recovery boiler 1 is separated, and a steam turbine plant 3 is independently provided. A gas turbine combustor 4 is provided with a heat exchanger 5, and a heated water generated from an economizer 6 of the exhaust heat recovery boiler 1 is used as a heating source to be supplied to the heat exchanger 5, and thus, a heat exchange of a fuel F supplied to the gas turbine combustor 4 is made to increase a quantity of heat.
As described above, in the Japanese Patent No. 2540646, efforts have been made to reduce fuel consumption and to improve a plant heat efficiency because there is an anxiety that fossil fuel resources are exhausted in near future.
In the prior art shown in FIG. 29, a heated water on an outlet side of the economizer 6 having a relatively small influence on load fluctuation is used as a heating source of the heat exchanger 5 so as to heat the fuel F, and then, a gas turbine driving gas (main flow gas) having the same temperature is generated by a fuel flow rate relatively smaller that that of the conventional case, and thus, a plant heat efficiency is improved. However, the heated water on the outlet side of the economizer 6 has been used as a heating source of the fuel F, and for this reason, there have arisen several problems.
Primarily, the temperature of heated water generated from the economizer 6 is set on the basis of heat balance of the whole plant regardless of heating the fuel F. For this reason, the temperature of the heated water becomes high by heating the fuel, and then, a saturation pressure based on the high temperature of heated water excessively becomes high. Thus, a feed water pump 6a requires a high pressure rising force, and thus, this is a factor of increasing the cost.
During partial load operation, when a flow rate of the heat water supplied to the heat exchanger 5 becomes low, a quantity of feed water from the feed water pump 6a passing through the economizer 6 becomes low. In this case, however, an internal pressure of the feed water pump rises, and for this reason, the heat water discharged from the economizer 6 exceeds a saturation temperature. As a result, there is the possibility that steaming is generated.
Further, the heated water of the economizer 6 is used as a heating source of the fuel F. In this case, however, the aforesaid construction is applied to only the combined cycle power generation plant. For example, in the case of a simple cycle gas turbine, it is difficult to secure a heating source, and for this reason, there has been required a gas turbine plant which can readily secure the heating source.
As described above, the prior art shown in FIG. 29 can improve the plant heat efficiency, but provides the aforesaid several problems.